1. Field of the Invention
The present invention relates generally to the generation of steam via the use of a combustion process to produce heat and, in one embodiment, to a device, system and/or method that enables one to control one or more process parameters of a combustion process so as to yield at least one desirable change in at least one downstream parameter. In one embodiment, the present invention is directed to a system and/or method for controlling at least one process parameter of a combustion process so as to yield at least one desirable change in at least one downstream process parameter associated with one or more of a wet flue gas desulfurization (WFGD) unit, a particulate collection device and/or control of additives thereto and/or a nitrogen oxide control device and/or control of additives thereto and/or additives to the system. In another embodiment, the present invention is directed to a system and/or method for controlling at least two process parameters of a combustion process so as to yield at least one desirable change in at least one downstream process parameter associated with one or more of a wet flue gas desulfurization (WFGD) unit, a particulate collection device and/or control of additives thereto and/or a nitrogen oxide control device and/or control of additives thereto and/or additives to the system.
2. Description of the Related Art
A variety of SO2 control processes and technologies are in use and others are in various stages of development. Commercialized processes include wet, semidry (slurry spray with drying) and completely dry processes. The wet flue gas desulfurization (WFGD) scrubber is the dominant worldwide technology for the control of SO2 from utility power plants, with approximately 85 percent of the installed capacity, although the dry flue gas desulfurization (DFGD) systems are also used for selected lower sulfur applications.
Wet scrubbing processes are often categorized by reagent and other process parameters. The primary reagent used in wet scrubbers is limestone. However, any alkaline reagent can be used, especially where site-specific economics provide an advantage. Other common reagents are lime (CaO), magnesium enhanced lime (MgO and CaO), ammonia (NH3), and sodium carbonate (Na2CO3).
A number of the wet processes are also classified as either non-regenerable or regenerable systems. In non-regenerable systems, the reagent in the scrubber is consumed to directly generate a byproduct containing the sulfur, such as gypsum. In regenerable systems, the spent reagent is regenerated in a separate step to renew the reagent material for further use and to produce a separate byproduct, such as elemental sulfur. The dominant limestone and lime reagent systems used today are non-regenerable. In many cases the regenerable systems have been retrofitted with non-regenerable limestone or lime reagent systems to reduce costs and improve unit availability.
As known to those of skill in the art, the most common WFGD absorber module is the spray tower design (see, e.g., Steam/its generation and use, 41st Edition, Kitto and Stultz, Eds., Copyright 2005, The Babcock & Wilcox Company, Barberton, Ohio, U.S.A., particularly Chapter 35—Sulfur Dioxide Control, the text of which is hereby incorporated by reference as though fully set forth herein). In the most common WFGD set-up the flue gas enters the side of the spray tower at approximately its midpoint and exits through a transition at the top. The upper portion of the module (absorption zone) provides for the scrubbing of the flue gas to remove the SO2 while the lower portion of the module serves as an integral slurry reaction tank (also frequently referred to as the recirculation tank (or absorber recirculation tank) and oxidation zone) to complete the chemical reactions to produce gypsum. The self-supporting absorber towers typically range in diameter from 20 feet to 80 feet (6 meters to 24 meters) and can reach 150 feet (46 meters) in height. In some designs, the lower reaction tank is flared downward to provide a larger diameter tank for larger slurry inventory and longer retention time. Other key components include the slurry recirculation pumps, interspatial spray headers and nozzles for slurry injection, moisture separators to minimize moisture carryover, oxidizing air injection system, slurry reaction tank agitators to prevent settling, and the perforated tray to enhance SO2 removal performance.
It has been found that higher concentrations (generally above about 700 ppm) of one or more oxidizers including, but not limited to persulfate, permanganate, manganate, ozone, hypochlorite, chlorate, nitric acid, iodine, bromine, chlorine, fluorine, or combinations of any two or more thereof, coupled with thermodynamically favorable pH and oxidation-reduction potential (ORP) (generally above 500 mV) conditions in the wet scrubber, will cause soluble manganese (Mn2+) to form MnxOy precipitate, as well as impact upon the nature, the amount and/or the conditions of mercury reemission and selenium emission from the WFGD. Additionally, the ORP in a WFGD can impact emission rate and/or phase partitioning and/or nature of one or more other compounds, or species. Additionally, the ORP in a WFGD absorber tank can influence the oxidation state of any selenium that is present in the absorber tank thereby impacting the ability of to control the emission of one or more selenium species. Generally speaking, an ORP of greater than about 300 mV in an ART tends to favor the formation of selenium (VI) species and/or compounds (e.g., selenate ions and/or compounds, etc.).
Additionally, the control of various Air Quality Control Systems (AQCS) are in need of optimization. As more and more power generation utilities are beginning to vary megawatt (MW) output, the boilers, SCRs, SNCRs, bag houses, ESPs and WFGD are being “asked” to fluctuate performance to respond to these changes in load. Thus, there is a need for various optimization programs that will permit for a more efficient use of ammonia, power input in the ESPs, limestone and/or lime injection into the WFGD or DFGDs and a potential for a higher quality gypsum byproduct.
Given the above, a need exists in the art for a system and/or method by which to control one or more process parameters of a combustion process so as to yield a favorable change in and/or permit the control of the ORP of a WFGD absorber tank thereby resulting in the ability to control one or more the downstream parameters so as to positively impact the ORP in the absorber tank of a WFGD unit, improve the operation of a WFGD unit, or improve, mitigate and/or control the emission of one or more species or compounds that occur from or downstream of a WFGD unit. Additionally a need exists to control the parameters of the various AQCS equipment to allow for one or more holistic optimization programs for one or more portions, of the totality, of an AQCS.